1. Field of the Invention
This invention relates to a method of regenerating and re-using a waste photographic processing solution and particularly, it is concerned with the way of arranging ion exchange membranes in an electrodialyzer which is employed for regenerating a waste photographic processing solution by the removal of bromine ion and/or iodine ion from the waste solution when the photographic processing solution is a developing solution for a silver halide photosensitive material, and by the removal of silver ion, halide ions and so on from the waste solution when the processing solution is a bleaching-fixing solution for a silver halide photosensitive material, or the like using the ion exchange membrane electrodialysis.
More particularly, the present invention relates to a method of regenerating waste photographic processing solutions through the ion exchange membrane electrodialysis method in which the ion exchange membranes used have an improved life-span, and wherein the regeneration work can be carried out safely and with high efficiency.
2. Description of the Prior Art
When optically exposed silver bromide, silver iodide, and/or silver chloride in emulsion layers of a sensitive material is reduced with a developing agent in a photographic developing solution in a developing process, a silver image is formed in the emulsion layers, and, at the same time, the oxidation product of the developing agent and bromine ion, iodine ion and/or chlorine ion are yielded as by-products therein.
As the bromine ion and/or the iodine ion yielded as the by-product in the developing process is accumulated in the waste solution of the developing solution, it adversely affects the photographic characteristics. Therefore, in order to regenerate the waste developing solution to enable the re-use thereof, the removal of these halide ions from the waste developing solution must be effected.
The developing process of a color photographic light sensitive material includes desilvering both the silver image formed by redox reactin with a developing agent and optically unexposed silver halides using a bleaching solution, and, subsequently, a fixing solution, or using a bleaching-fixing solution to finally obtain the color image alone.
In the bleach-fixation processing of color photographic light sensitive materials, silver thiosulfate and halide ions are accumulated in the bleaching-fixing solution, and a part of an organic acid-Fe(III) complex ion is converted into the corresponding organic acid-Fe(II) complex ion, resulting in a decrease in the power to oxidize silver; therefore the removal of both of the abovedescribed salt and ions from the waste bleaching-fixing solution and the oxidation of the Fe(II) complex ion for the purpose of conversion into the corresponding Fe(III) complex ion are indispensable for the re-use of the waste bleaching-fixing solution through a regeneration process.
Methods of removing halide ions from the waste solution of photographic developing solutions and of removing silver thiosulfate and halide ions from the waste solution of bleaching solutions have included ion exchange membrane electrodialysis, in which electrodialysis is carried out using an electrodialyzer. In such cells, the space between a cathode and an anode is partitioned by cation exchange membranes and anion exchange membranes alternately to form, in the direction from the cathode to the anode, a cathode compartment, an alternately arranged plurality of desalting compartments (in which each compartment is partitioned by a cation exchange membrane on the cathode side and by an anion exchange membrane on the anode side) and of concentrating compartments (in which each compartment each is partitioned by an anion exchange membrane on the cathode side and by a cation exchange membrane on the anode side), and an anode compartment. The method involves pouring a waste developing solution into the desalting compartments, and a sodium sulfate solution or a sodium carbonate solution into the concentrating compartments, and then passing a direct current between the cathode and the anode. For instance, experimental data regarding the removal of bromine ion from a waste developing solution under the conditions wherein the current density of an ion exchange membrane is adjusted at from 0.50 A/dm.sup.2 to 2.0 A/dm.sup.2 are reported in S. Mizusawa, A. Sasai and N. Mii, Bulletin of the Society of Scientific Photography of Japan, No. 18 (December), pages 38-44 (1968).
In addition, methods of regenerating photographic developing solutions by means of ion exchange membrane electrodialysis are also described in published unexamined Japanese Patent Application (OPI) Nos. 97432/'76 and 85722/'76 (std. OPI def.), and in published examined Japanese Patent Application 34940/'77. Moreover, another method is also known, as described in Japanese Patent Application (OPI) Nos. 46732/'78, 8626/'79 and 19741/'79, in which a contact treatment with a polymer or a resin is conducted before or simultaneously with the dialysis of the waste developing solution with the intention of improvement upon the efficiency of the above-described regeneration methods and continuation of the life-span of the membranes used in electrodialysis.
A method of regenerating the waste solution of a photographic bleaching-fixing solution by ion exchange membrane electrodialysis is described in Japanese Patent Application (OPI) No. 60371/'78.
However, in each of the above-described methods, the arrangement of ion exchange membranes in an ion exchange membrane electroldialytic cell consists only of combinations of the anion exchange membranes and cation exchange membranes as shown in FIG. 1 and FIG. 2 hereinafter.
In the electrode compartments of these electrodialytic cells, solutions of electrolytes such as sodium sulfate, sodium hydroxide, potassium hydroxide and sulfuric acid, are usually employed. Although useful, the above-described methods suffer from serious defects as described below.
One of such defects occurs when the membranes are arranged in a combination as shown in FIG. 1, and a solution for concentration compartments, a solution for electrode compartments and a waste developing solution are made to flow through their respective pathways shown in FIG. 1.
With respect to the solution supplied to the electrode compartments, anions dialyzed when the solution passes through the cathode compartment, and cations are dialyzed when the solution passes through the anode compartment. Consequently, the concentration of the electrolyte in the solution decreases, causing an increase in electric resistance, whereby ultimately it becomes impossible to continue electrodialysis. Therefore, supplementing to make up for the decreased concentration of the electrolyte is required for the continuous operation of regeneration. However, such supplementing procedures are troublesome and an inconvenience.
On the other hand, in a regeneration method wherein an cathode and an anode are connected with each other through membranes having an arrangement as shown in FIG. 2, which arrangement is disclosed in Japanese Patent Application (OPI) No. 97432/'76, though it does not suffer the above-described disadvantage caused in the method as illustrated in FIG. 1, suffers from the defect that bromine ion is permeated into the anode compartment by dialysis, and is oxidized therein to produce bromine gas.